In many printing and/or xerography systems, images can be formed by fusing a dry marking material such as toner to a paper sheet and/or other medium using electrophotographic printing. Fusing occurs when the paper is subjected to pressure and heat to permanently affix the toner to the paper. Most common printers can utilize fuser rolls and pressure rolls that form a nip for the paper to pass through for producing the print images. The printing and/or xerography systems are normally provided with replaceable parts and/or components, which is a common failure mode. In such printers, a variety of different size sheets can be passed through the nip of the rolls, so that the fuser rolls are subjected to wear. In particular, edge wear is a leading fusing failure mode regardless of print engine type, i.e. mono or color, or market segments.
Wear is a process of gradual removal of a material from surfaces of solids subject to contact and sliding. All conformable fuser rolls suffer from surface wear, especially when the edges of the sheets contact the fuser roll surface. Such surface wear can exhibit a variety of wear patterns including abrasion, fatigue, corrugation, erosion, etc. For example, the edges of 11″ and 14″ sheets of paper are distributed along the surface of the fuser rolls in an axial direction in the printers without a Registration Distribution System (RDS). In such case, the paper edges can produce a stress concentration and a sheet-roll velocity differential, which degrade the thin surface coating on the fuser rolls and the elastomeric layer under the fuser roll surface. The mixed paper sizes can also produce a differential gloss streak, i.e. edge gloss, from the outboard edge. The degradation of the fuser rolls can exhibit a narrow area of lower gloss from a lead edge to a trail edge across the print fused to the paper. Such component wear is visible to the customer after a few thousand prints passed through the fuser, which degrade the service life of the fuser rolls.
In some prior art printing systems, an intelligent fusing station can be utilized for detecting incoming paper size in order to reposition the fuser roll in an axial direction based on usage demographics, such that the location of edge wear is spread over a larger area. The intelligent fusing station can be moved by a stepping-type drive motor controlled by a control and logic circuit. This way, a discrete location within the 3 inches of roll from the 11 inch position to the 14 inch position can be made available for edge redistribution, when the paper run is 11 inches wide. However, such systems can increase the printer cost and also slow down the printing productivity due to the necessity to move the paper to the fusing station during a printing operation. For example, the fuser rolls can suffer unnecessary wear at the point where the edges of the paper sheets contact the roll surface due to the movement of the fusing station. In addition, banding can also result from the utilization of such intelligent systems, which severely limit printing performance.
Referring to FIG. 1, labeled as “prior art”, a schematic diagram of a graph 100 of sheet edge density distribution over a fuser roll surface is illustrated. All conformable fuser rolls (not shown) can suffer from surface wear, especially when the edges of the paper sheets contact the surface of the fuser rolls. The edge wear occurs when the paper edges pass through a fuser nip under pressure, which degrades the thin surface coating on the fuser roll and the elastomer layer under the fuser roll surface due to a stress concentration and a sheet-roll velocity differential. Such degradation can accumulate and eventually manifest itself on larger media prints as a gloss streak, also known as edge gloss.
The perceptibility of edge wear induced gloss streaks depends on the distribution of paper edges on the fuser roll surface. The gloss differential is perceptible when the edge density passes a certain threshold or peak 101. In addition, a slope 102 of the edge density distribution, i.e. a transition between worn and non-worn areas 103 of the fuser roll, also drives perceptibility as shown in FIG. 1. Sharp transitions, i.e. steep slope, from the worn and non-worn areas 103 can be perceived more readily than smooth transitions. Thereafter, the system can spread out the edge density distribution by dithering the position of the paper edge relative to the fuser roll surface in order to increase the edge wear life of a fuser roll. Such systems move the fuser roll back and forth in an axial direction, i.e. inboard to outboard, to redistribute the edge density distribution. However, such system can also suffer from real time measurements.
The majority of prior art printing systems exhibit an open problem in detection of the level of component wear in situ and in real time. One of the printing systems can measure the gloss on the fuser roll surface by scanning a point optical sensor back and forth over the fuser rolls. But, such printing systems can degrade the printing resolution. Some systems utilize fluorescent tags of toner particles for concentration measurement and detection of unauthorized components in photocopying machines, and also invisibly mark fuser belts with fluorescent ink to allow detection. Such fluorescent toners can be proposed in a variety of applications such as security and anti-counterfeiting applications, automatic density controller, toner concentration control, detection of image misregistration in tandem engines, and presence of transparency sheets in paper path. But, no prior art print engines are taught that track and analyze the fuser roll/belt edge wear in real time with higher resolution.
A need therefore exists for an improved optical measurement system and method for determining a wear level of printer components, which provides real time measurements and are also implemented in situ. Such an improved system and method are described in greater detail herein.